U.S. patent application number 17/425306 was filed with the patent office on 2022-03-31 for torsion shear bolt for electric junctions.
The applicant listed for this patent is CEMBRE S.P.A.. Invention is credited to Gualtiero BAREZZANI.
Application Number | 20220099131 17/425306 |
Document ID | / |
Family ID | |
Filed Date | 2022-03-31 |
![](/patent/app/20220099131/US20220099131A1-20220331-D00000.png)
![](/patent/app/20220099131/US20220099131A1-20220331-D00001.png)
![](/patent/app/20220099131/US20220099131A1-20220331-D00002.png)
![](/patent/app/20220099131/US20220099131A1-20220331-D00003.png)
![](/patent/app/20220099131/US20220099131A1-20220331-D00004.png)
![](/patent/app/20220099131/US20220099131A1-20220331-D00005.png)
![](/patent/app/20220099131/US20220099131A1-20220331-D00006.png)
United States Patent
Application |
20220099131 |
Kind Code |
A1 |
BAREZZANI; Gualtiero |
March 31, 2022 |
TORSION SHEAR BOLT FOR ELECTRIC JUNCTIONS
Abstract
A shear bolt for a junction of electrical conductors includes a
tool seat for engagement of the shear bolt by a screwing tool, an
externally threaded portion to be screwed in a terminal body of the
junction, along a screwing axis, and a tightening portion for
engaging an electrical conductor to be tightened in the terminal
body. The tool seat is formed at the threaded portion and the
tightening portion is connected to the threaded portion on an
opposite side with respect to the tool seat. The shear bolt can be
sheared in one or more programmed rupture areas in the threaded
portion when exceeding a predetermined tightening torque for each
of the programmed rupture areas, respectively. Even with the screw
unscrewed, the tightening portion is connected to the threaded
portion and is rotatable with respect to the threaded portion about
the screwing axis and non-detachable from the threaded portion.
Inventors: |
BAREZZANI; Gualtiero;
(Brescia, IT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CEMBRE S.P.A. |
Brescia |
|
IT |
|
|
Appl. No.: |
17/425306 |
Filed: |
February 5, 2020 |
PCT Filed: |
February 5, 2020 |
PCT NO: |
PCT/IB2020/050924 |
371 Date: |
July 22, 2021 |
International
Class: |
F16B 31/02 20060101
F16B031/02; H01R 4/36 20060101 H01R004/36 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 5, 2019 |
IT |
102019000001625 |
Claims
1-23. (canceled)
24. An electrical junction device (2) comprising: A) a metal
terminal body (6) with: at least one axial hole (21) which is open
on an outer side of the terminal body (6) and adapted to
accommodate an electrical conductor end (3), one or more
transversal holes (22) at the axial hole (21), said transversal
holes (22) being internally threaded, open on a lateral side of the
terminal body (6) and leading into the axial hole (21), B) a
plurality of shear bolts (1) which can be screwed into the
transversal holes (22) to lock the electrical conductor end (3) in
the axial hole (21), wherein: the terminal body (6) forms a
cylindrical outer surface (23), a cap seat (24) adapted to receive
a cap (27) of the electrical junction (2) is formed in the
cylindrical outer surface (23) at each transversal hole (22), and
the cap (27) forms an outer surface (32) having the same curvature
as the curvature of the cylindrical outer surface (23) of the
terminal body (6).
25. The electrical junction device (2) of claim 24, wherein: the
cap seat (24) forms a substantially planar bottom (25), in which
the transversal hole (22) opens, and two opposite positioning
surfaces (26) transversal to the bottom (25), the cap (27)
comprises a closing portion (28) having a shape which is
complementary to the shape of the cap seat (24), the closing
portion (28) forms a planar support surface (30) resting on the
bottom (25) of the cap seat (24), and two opposite
counter-positioning surfaces (31) transversal to the support
surface (30), positioned or facing against the positioning surfaces
(26) of the cap seat (24), as well as said outer surface (32)
opposite the support surface (30) and having said curvature which
is identical to the curvature of the cylindrical outer surface (23)
of the terminal body (6), with the cap (27) being positioned in the
cap seat (24), the outer surface (32) of the closing portion (28)
makes a cylindrical continuity of the cylindrical outer surface
(23) of the terminal body.
26. The electrical junction device (2) of claim 25, wherein the
shape and position of the positioning surfaces (26) and the shape
and position of the counter-positioning surfaces (31) are such as
to allow the insertion of the closing portion (28) into the cap
seat (24) only in a predetermined relative position.
27. The electrical junction device (2) of claim 26, wherein the
closing portion (28) has an extension parallel to the support
surface (30) in the extension direction of the counter-positioning
surfaces (31), which is greater than a distance between the two
counter-positioning surfaces (31).
28. The electrical junction device (2) of claim 25, wherein both
the closing portion (28) and the cap seat (24) are rectangular in
shape.
29. The electrical junction device (2) of claim 25, wherein: along
two first opposite sides of the closing portion (28), the outer
surface (32) and the support surface (30) are spaced apart from
each other by the counter-positioning surfaces (31), and along two
second opposite sides of the closing portion (28), the outer
surface (32) and the support surface (30) meet at a common edge
with an acute angle, along two first opposite sides of the cap seat
(24), the bottom (25) of the cap seat (24) and the cylindrical
outer surface (23) of the terminal body (6) are spaced apart from
each other by the positioning surfaces (26), and along two second
opposite sides of the cap seat (24), the bottom (25) and the
cylindrical outer surface (23) meet at a common edge with an obtuse
angle.
30. The electrical junction device (2) of claim 24, wherein the cap
(27) forms an anchoring protrusion (29) which can be inserted, by
interference, into a longitudinal hole (12) of the shear bolt (1)
screwed in the transversal hole (22).
31. The electrical junction device (2) of claim 24, wherein the
caps (27) are made of an electrically conducting polymer material
selected from the group consisting of extrinsically conducting
polymers and intrinsically conducting polymers.
32. The electrical junction device (2) of claim 24, said shear bolt
(1) comprising: a tool seat (4) for the engagement of the shear
bolt (1) by means of a screwing tool, an externally threaded
portion (5) intended to be screwed in a terminal body (6) of the
junction (2), along a screwing axis (7), a tightening portion (8)
intended to engage an electrical conductor (3) to be tightened in
the terminal body (6), wherein the tool seat (4) is formed at the
threaded portion (5) and the tightening portion (8) is connected to
the threaded portion (5) on an opposite side with respect to the
tool seat (4), wherein the shear bolt (1) can be sheared in one or
more programmed rupture areas (9, 9', 9'') in the threaded portion
(5) when exceeding a predetermined tightening torque for each of
the programmed rupture areas (9, 9', 9''), respectively, and
wherein, even with the screw (1) unscrewed, the tightening portion
(8) is connected to the threaded portion (5) so as to be able to
rotate with respect to the threaded portion (5) about the screwing
axis (7) and so as to be non-detachable from the threaded portion
(5).
33. The electrical junction device (2) of claim 32, wherein the
tightening portion (8) forms a tightening surface (10) facing in an
opposite direction with respect to the tool seat (4) and intended
to make the contact with the electrical conductor (3), said
tightening surface (10) being continuous and domed in a convex
manner.
34. The electrical junction device (2) of claim 33, wherein the
tightening surface (10) forms an axial-symmetrical spherical
surface segment with respect to the screwing axis (7).
35. The electrical junction device (2) of claim 32, wherein the
threaded portion (5) forms a longitudinal hole (12) which is open
on an opposite side with respect to the tightening portion (8).
36. The electrical junction device (2) of claim 35, wherein the
longitudinal hole (12) is a through hole which is also open on a
front end (14) of the threaded portion (5) facing the tightening
portion (8), and the longitudinal hole (12) makes an
anti-extraction and hinge seat (15) for the tightening portion
(8).
37. The electrical junction device (2) of claim 36, wherein: the
anti-extraction seat (15) forms a hole portion (17) with a smaller
inner diameter than the inner diameter of a directly bordering
portion of the longitudinal hole (12), as well as an inner shoulder
(16) facing the tool seat (4), the tightening portion (8) forms a
pin (18) having an enlarged end (19), wherein the pin (18) is
inserted into the hole portion (17) with a smaller diameter and the
enlarged end (19) is trapped by the inner shoulder (16) in order to
prevent the tightening portion (8) from detaching from the threaded
portion (5).
38. The electrical junction device (2) of claim 32, comprising: a
sliding interface (20), formed by two opposite planar sliding
surfaces (20', 20'') having a mutual maximum allowable distance
determined by an anti-extraction support of a locally enlarged
anchoring portion (19) of the tightening portion (8) against a
locally narrowed hooking portion (16, 17) of the threaded portion
(5), even with the screw (1) unscrewed, and/or a third element (33)
interposed between the threaded portion (5) and the tightening
portion (8), and/or an anti-friction material layer (34) interposed
between the threaded portion (5) and the tightening portion (8),
and/or an elastic member (35) interposed between the threaded
portion (5) and the tightening portion (8).
Description
[0001] The invention relates to a fastening device for making of an
electrical contact, in particular, a torsion shear bolt (sometimes
called "shear pin") with a tightening portion which can be
separated by rupturing from a tool engagement portion.
[0002] In the sector of power lines, jointing by screwing is known
to provide a metal terminal body (made of electrically conductive
material) forming two opposite axial holes, which are open on two
opposite sides of the terminal body and each adapted to accommodate
one end of respectively two electrical conductors to be connected
electrically and mechanically to each other. Furthermore, the
terminal body forms, at each of the two axial holes, one or more
transversal threaded holes, which are open on a lateral side of the
terminal body and leading into the axial hole, either transversally
or radially. The aforesaid torsional shear bolts can be screwed
into the transversal holes, in order to engage and lock the ends of
the electrical conductors positioned in the axial holes and, in
this manner, make both the electrical contact and the mechanical
connection between the two electrical conductors.
[0003] Similarly, it is known to provide a metal terminal body
(made of electrically conductive material) in the cable lugs
forming a connection portion and an axial hole, open on one side
opposite to the connection portion and adapted to accommodate one
end of an electrical conductor to be electrically connected to the
terminal body. Furthermore, the terminal body forms, at the axial
hole, one or more transversal threaded holes, which are open on a
lateral side of the terminal body and leading into the axial hole,
either transversally or radially. The aforesaid torsional shear
bolts can be screwed into the transversal holes, in order to engage
and lock the end of the electrical conductor positioned in the
axial hole and, in this manner, make both the electrical contact
and the mechanical connection between the electrical conductor and
the terminal body.
[0004] Layers of insulating material, e.g. polymer insulation
sheaths, are applied about the terminal body after screwing and
shearing (by tightening with a torque greater than a torsional
resistance) of the shear bolts.
[0005] In order to have a sufficient threading engagement length
for reliable tightening, the need is felt for the shear bolts to
make a sheared surface which is as close to the outer end of the
terminal body threading as possible. On the other hand, in order to
allow the correct reconstruction of the insulation in the area of
the electrical and mechanical junction, the need is felt that the
shear bolts (and their sharp edges) do not protrude beyond the
outer surface of the terminal body after shearing.
[0006] WO 96/31706 describes an electrical junction with torsion
shear bolts provided with discrete rupture areas formed by notches
in the bolt, the shearing torque (shearing resistance) of which
increases from a front area facing towards the electrical conductor
to a head area (tool engagement seat) of the bolt. In this manner,
with a shear bolt screwed into the threading of the terminal body,
the shearing is performed at the programmed rupture notch furthest
from the bolt head and not completely inserted into (and therefore
stabilized by) the threading of the terminal body.
[0007] The tightening force of such shear bolts, acting on an
electrical conductor to be tightened, is influenced by the
combination of the friction in the threading during the screwing
and the friction of the head against the conductor. If the head
friction, which depends on the friction coefficient between the
material of the bolt and the material of the electrical conductor,
becomes too great, the bolt may be sheared at a tightening force
which is too low and therefore the desired long-term conservation
of the tightening force will not be ensured.
[0008] Furthermore, the rotation of the tip of the shear bolt
pressing against the conductor provides a milling effect that
damages the conductor and further impairs the long-term contact
force.
[0009] For this reason, in the prior art, the friction behavior is
regulated by using lubricants or coatings of the shear bolt, making
the manufacture more expensive and, however, not being able to
ensure the safety of operation in all areas of application, e.g. in
case of long service life and significant temperature
variations.
[0010] EP1911981B1 discloses a shear bolt having a threaded portion
which can be screwed onto the terminal body and a tightening
portion destined to engage the electrical conductor to be
tightened, in which the tightening portion is formed in one piece
with the threaded portion. The shear bolt can be sheared in the
threaded portion (first rupture point) upon reaching a first
tightening torque and, in addition, the tightening portion can be
sheared and separable from the threaded portion (second rupture
point) upon reaching of a second tightening torque, combined with a
corresponding axial tightening force, wherein the second tightening
torque is lower than the first tightening torque in order to allow,
after the rupture of the tightening portion, a rotation of the
threaded portion with respect to the tightening portion which can
press on the conductor without relative rotations between them.
[0011] This known solution works satisfactorily only on the
condition that the two screwing torques which distinguish the first
rupture from the second rupture are sufficiently far apart and of a
sure value. This requires precision machining of the rupture area
of the tightening portion and makes the bolt usable only for a
limited range of threads and tightening torques.
[0012] The second tightening torque, which determines the rupture
of the tightening portion, inevitably and significantly varies
according to the type (material, single wire, strand, diameter) of
conductor used and, therefore, there is no certainty about the real
operation of the bolt and the moment in which the milling effect on
the conductor ceases. Indeed, after partial milling of a strand,
individual conductor fibers may interfere with the relative rotary
movement between the threaded portion and the tightening portion
and, therefore, also influence the first screwing torque which
causes the bolt to rupture in the threaded portion.
[0013] Finally, the rupturing ease of the tightening portion
implies the risk that, when a shear bolt is partially screwed into
the transversal hole of the terminal body, during the insertion of
the conductor into the axial hole, the tip of the conductor pushes
against the tightening portion, detaching it from the bolt and
displacing it to an unexpected position which makes the tightening
bolt unusable.
[0014] It is the object of the present invention to provide a shear
bolt for an electrical conductor junction device and a junction
device for electrical conductors which overcome the drawbacks of
the prior art.
[0015] It is a particular object of the invention to make a
junction of electrical conductors suited for long service life,
which is mechanically stable and capable of transmitting electrical
current, regardless of the material of the electrical conductor
used.
[0016] It is a further particular object of the invention to
further reduce the milling effect on the conductor.
[0017] It is a further object of the invention to reduce the number
of precision machining operations on the shear bolt.
[0018] These and other objects are achieved by means of a shear
bolt according to claim 1. The dependent claims relate to
advantageous and preferred embodiments of the invention.
[0019] According to an aspect of the invention, a shear bolt for a
junction of electrical conductors comprises:
[0020] a tool seat for the engagement of the shear bolt by means of
a screwing tool,
[0021] an externally threaded portion intended to be screwed in a
terminal body of the junction, along a screwing axis,
[0022] a tightening portion intended to pressure engage an
electrical conductor to be tightened in the terminal body,
[0023] wherein the tool seat is formed at the threaded portion and
the tightening portion is connected to the threaded portion on an
opposite side with respect to the tool seat,
[0024] wherein the shear bolt can be sheared in one or more
programmed rupture regions in the threaded portion when exceeding a
predetermined tightening torque for each of the programmed rupture
areas, respectively,
[0025] wherein the tightening portion is connected to the threaded
portion so as to:
[0026] be able to rotate with respect to the threaded portion about
the screwing axis and
[0027] not to be separable or detachable from the threaded
portion.
[0028] This allows the shear bolt to operate satisfactorily
regardless of the value of the tightening torques which determine
the programmed rupture of the threaded portion of the bolt, avoids
the need for precision machining to create a special rupture area
of the tightening portion, and makes the shear bolt usable without
limitations with respect to the threading type and to the
tightening torque value.
[0029] The shear bolt allows relative rotation between the
tightening portion and the threaded portion from the first contact
with the conductor, regardless of the type (material, single wire,
strand, diameter) of conductor used, reliably avoiding the milling
effect on the conductor.
[0030] This ensures the development of a high contact force and, at
the same time, maintains the integrity of the electrical conductor,
thus creating a connection suitable for long service life, which is
mechanically stable and capable of transmitting electrical current,
regardless of the material of the electrical conductor used.
[0031] In order to better understand the invention and appreciate
its advantages, the description of some embodiments will be
provided below by way of non-limiting examples with reference to
the figures, in which:
[0032] FIG. 1 is a longitudinal section view of a shear bolt
according to an embodiment,
[0033] FIG. 2 is an enlarged view of a detail in FIG. 1,
[0034] FIGS. 3 and 4 are perspective views of the shear bolt
according to embodiments,
[0035] FIG. 5 is a cross-section view of an electrical junction
during the step of screwing of the shear bolt (in longitudinal
section) against an electrical conductor accommodated in a terminal
body of the junction,
[0036] FIG. 6 is a cross-section view of the electrical junction in
FIG. 5 at the end of the step of screwing and after the programmed
rupture of the shear bolt,
[0037] FIG. 7 is an exploded view of an electrical junction device
according to an embodiment,
[0038] FIG. 8 is a longitudinal section view of the electrical
junction device in FIG. 7 in a step of screwing of the shear
bolts,
[0039] FIG. 9 shows the electrical junction device in FIG. 5 at the
end of the step of screwing and after the programmed rupture of the
shear bolts,
[0040] FIG. 10 is a perspective view of the electrical junction
completed by means of closing caps, but not yet covered by external
insulating layers, according to an embodiment,
[0041] FIGS. 11, 12, 13 are perspective views of a closing cap for
the electrical junction device according to an embodiment,
[0042] FIG. 14 is a longitudinal section view of the electrical
junction in FIG. 10,
[0043] FIG. 15 is an exploded view of an electrical junction
device, forming a terminal, according to an embodiment,
[0044] FIG. 16 is a perspective view of the electrical junction in
FIG. 15 completed by means of closing caps, but not yet covered by
external insulating layers, according to an embodiment,
[0045] FIG. 17 is a longitudinal section view of the electrical
junction device in FIG. 15 in a step of screwing of the shear
bolts,
[0046] FIG. 18 shows the electrical junction device in FIG. 15 at
the end of the step of screwing and after the programmed rupture of
the shear bolts,
[0047] FIG. 19 shows the electrical junction device in FIG. 18 with
closing caps,
[0048] FIGS. 20 and 21 are section views of shear bolts according
to further embodiments,
[0049] FIGS. 22 and 23 are section and perspective views of a shear
bolt according to a further embodiment.
[0050] With reference to the figures, a shear bolt 1 for a junction
2 of electrical conductors 3, comprises;
[0051] a tool seat 4 for the engagement of the shear bolt 1 by
means of a screwing tool (not shown),
[0052] an externally threaded portion 5 intended to be screwed in a
terminal body 6 of the junction 2, along a screwing axis 7 (which
corresponds to the longitudinal axis of the screw 1),
[0053] a tightening portion 8 intended to engage by pressing an
electrical conductor 3 to be tightened in the terminal body 6,
[0054] wherein the tool seat 4 is formed at the threaded portion 5
and the tightening portion 8 is connected to the threaded portion 5
on an opposite side with respect to the tool seat 4,
[0055] wherein the shear bolt 1 can be sheared in one or more
programmed rupture areas 9, 9', 9'' in the threaded portion 5 when
exceeding a predetermined tightening torque for each of the
programmed rupture areas 9, 9', 9'', respectively,
[0056] wherein (even with the screw 1 unscrewed), the tightening
portion 8 is connected to the threaded portion 5 so as to be able
to rotate with respect to the threaded portion 5 about the screwing
axis 7 and so as to be not separable or detachable from the
threaded portion 5.
[0057] This allows the shear bolt 1 to operate satisfactorily
regardless of the value of the tightening torques which determine
the programmed rupture of the threaded portion 5 of the bolt 1,
avoids the need for precision machining to create a special rupture
area of the tightening portion 8, and makes the shear bolt 1 usable
without limitations with respect to the threading type and the
tightening torque value.
[0058] The shear bolt 1 allows relative rotation between the
tightening portion 8 and the threaded portion 5 from the first
contact with the conductor 3, regardless of the type (material,
single wire, strand, diameter) of electrical conductor 3 used,
reliably avoiding the milling effect on the electrical conductor
3.
[0059] This ensures the development of a high contact force and, at
the same time, maintains the integrity of the electrical conductor
3, thus creating a connection suitable for long service life, which
is mechanically stable and capable of transmitting electrical
current, regardless of the material of the electrical conductor 3
to be tightened.
[0060] According to an embodiment, the tightening portion 8 forms a
tightening surface 10 facing in an opposite direction with respect
to the tool seat 4 and intended to make the contact with the
electrical conductor 3. Advantageously, the tightening surface 10
is continuous, but not planar, preferably domed in a convex manner,
e.g. with uniform curvature, preferably a spherical surface segment
(FIGS. 4, 5, 6), even more preferably the tightening surface 10 is
axial-symmetrical with respect to the screwing axis 7. This allows
to reduce the milling effects on the conductor 3 as much as
possible and, furthermore, increases the contact area between the
tightening surface 10 and the conductor clamped by it, resulting in
lower electrical contact resistance and a larger friction area with
greater anti-extraction resistance.
[0061] Furthermore, the domed shape of the tightening surface 10,
e.g. with respect to a planar surface, avoids the notching effect
on the electrical conductor 3 which would occur at the peripheral
edge of a planar surface.
[0062] According to an alternative embodiment, the tightening
surface is basically planar.
[0063] With additional advantage, a peripheral edge 11 formed about
the tightening surface 10 is further retracted with respect to the
latter, e.g. by means of a chamfering (FIGS. 1, 4).
[0064] According to an embodiment, the threaded portion 5 forms a
longitudinal hole 12, which is concentric with respect to the
screwing axis 7 and open on a side opposite to the tightening
portion 8. The longitudinal hole 12 may form the aforesaid tool
seat 4, e.g. a recessed hexagonal seat (FIG. 3) or a hexagonal head
with an external hexagon (FIGS. 22, 23), advantageously at a rear
end 13 (head) of the shear bolt 1. This allows the engagement of
the bolt 1 by means of a screwing tool in a region far from the
programmed rupture areas 9, 9', 9''.
[0065] The longitudinal hole 12 is preferably not threaded
internally to avoid additional notching effects which could
adversely affect the programmed rupture certainty in the programmed
rupture areas 9', 9', 9''.
[0066] However, the longitudinal hole 12 could be a frusto-conical
or a variable diameter stepped hole so as to define (or contribute
to the definition of) the positions of the programmed rupture areas
9, 9', 9''.
[0067] According to a preferred embodiment, the longitudinal hole
12 is a through-hole also open on a front end 14 of the threaded
portion 5, facing towards the tightening portion 8, and makes a
hinge- and anti-extraction-anchoring seat 15 (hereinafter
anti-extraction seat 15 for the sake of brevity) for the tightening
portion 8.
[0068] According to an embodiment, the anti-extraction seat 15
forms a hole portion 17 with a smaller inner diameter than the
inner diameter of a directly bordering portion of the longitudinal
hole 12, as well as an inner shoulder 16 facing the tool seat 4.
The tightening portion 8, in turn, forms a pin 18 having an
enlarged end 19 (e.g. outstretched or mushroom head). The pin 18 is
inserted into the hole portion 17 with a smaller diameter and the
enlarged end 19 is trapped by the inner shoulder 16 so as to
prevent the tightening portion 8 from detaching from the threaded
portion 5.
[0069] The engagement between the inner shoulder 16 of the
anti-extraction seat 15 and the enlarged end 19 of the tightening
portion 8 performs an additional important function. It determines
a maximum permissible thickness of a gap or sliding interface 20
between the tightening portion 8 and the threaded portion 5.
[0070] Such a sliding interface 20, formed between two,
advantageously planar and possibly lubricated, opposite sliding
surfaces 20', 20'' is preferably reduced (e.g. in the order of a
few tenths of a millimeter) to avoid the introduction of foreign
bodies or conductor strand fibers, or by only a few thousandths of
a millimeter to facilitate lubrication.
[0071] The tightening portion 8 is therefore preferably a
rotationally symmetrical body with a domed circular disc portion on
a front side and planar on a rear side and with the aforesaid pin
18 protruding from the rear side of the disc and ending at the
enlarged end 19.
[0072] According to an embodiment, the programmed rupture areas 9,
9', 9'' comprise annular cavities formed in an outer surface of the
threaded portion 5 and defining, together with the longitudinal
hole 12, portions (of material) of locally reduced section, the
shearing torques (shear resistance) of which increase going from
the front end 14 to the rear end 13 of the threaded portion 5.
[0073] In this manner, during the screwing of the shear bolt 1 into
the threading of the terminal body 6, the shearing is performed at
the programmed rupture notch furthest from the bolt head and not
completely inserted into and retained by the threading of the
terminal body 6.
[0074] Preferably, the bolt 1 forms three of said programmed
rupture areas 9', 9', 9''.
[0075] The bolt 1 is made of electrically conductive and preferably
corrosion-resistant metal material, e.g. brass.
[0076] The rotational connection of the tightening portion 8 to the
threaded portion 5, with respect to their manufacturing in one
piece, implies the additional advantage of being able to make the
two components of different materials, e.g. a tightening portion
material specifically suited to make electrical contact with the
electrical conductor 3 and a threaded portion material specifically
suited for the threaded engagement with the terminal body 6.
[0077] According to an embodiment, the shear bolt 1 comprises a
third element 33 interposed between the threaded portion 5 and the
tightening portion 8, e.g. a disc or layer of anti-friction
material 34 (FIG. 20) to lower the relative rotational friction, or
an elastic element 35 (FIG. 21) to recover clearance between the
tightening portion 8 and the threaded portion 5.
[0078] The metal terminal body 6 forms two opposite axial holes 21,
e.g. concentric, each open on respectively one of two opposite
sides of the terminal body 6 and adapted to accommodate an end of
electrical conductor 3. Furthermore, the terminal body 6 forms, at
each of the two axial holes 21, one or more transversal internally
threaded holes 22, which are open on a lateral side of the terminal
body 6 and leading into the axial hole 21, either transversally or
radially (FIGS. 7, 8).
[0079] The shear bolts 1 can be screwed into the transversal holes
22 to engage and lock the ends of the electrical conductors 3
positioned in the axial holes 21 and, in this manner, make both the
electrical contact and the mechanical connection between the two
electrical conductors 3.
[0080] Similarly, in the case in which the electrical junction
device 2 forms a lug 36 (FIGS. 15-19), the metal terminal body 6
forms an axial hole 21 which is open on the opposite side with
respect to a connection portion 37, e.g. ring-shaped or
open-mouthed, and adapted to accommodate an end of electrical
conductor 3. The terminal body 6 further forms one or more
internally threaded transversal holes 22 at the axial hole 21,
which are open on a lateral side of the terminal body 6 and leading
into the axial hole 21, either transversally or radially (FIG.
17-19).
[0081] The shear bolts 1 can be screwed into the transversal holes
22 to engage and lock the end of the electrical conductor 3
positioned in the axial hole 21 and, in this manner, make both the
electrical contact and the mechanical connection between the
electrical conductor 3 and the terminal body 6.
[0082] Layers of insulating material (not shown), e.g. polymer
insulation sheaths, are applied about the terminal body 6 after the
screwing and the shearing of the shear bolts 1.
[0083] In order to protect the external electrical insulation from
shearing edges of bolts 1, it is known to apply a protective cap
onto each bolt 1 and/or each transversal hole 22.
[0084] However, due to the curvature of the outer surface of the
terminal body 6 and the variability of the angular position of the
bolts 1, the caps of the prior art tipically do not match the outer
surface of the terminal body 6 precisely, forming steps or cavities
which create undesired gaps between the outer insulating layer and
the terminal body 6.
[0085] According to an embodiment, the terminal body 6 forms a
cylindrical outer surface 23, and at each transversal hole 22, a
cap seat 24 is machined in the outer surface 23 with a
substantially flat bottom 25, in which the transversal hole 22
opens, and two positioning surfaces 26, which are opposite and
transversal, e.g. perpendicular, to the bottom 25 (FIG. 7). The cap
seat 24 is adapted to accommodate a cap 27 (preferably made of
polymeric material) having a closing portion 28 of shape
complementary to that of the cap seat 24 and an anchoring
protrusion 29, which can be inserted by interference into the
longitudinal hole 12 of the bolt 1 screwed into the transversal
hole 22.
[0086] The closing portion 28 forms:
[0087] a planar support surface 30 intended to rest on the bottom
25 of the cap seat 24, and
[0088] two counter-positioning surfaces 31 opposite to each other,
which are transversal, e.g. perpendicular, to the support surface
30, and intended to be positioned or facing against the positioning
surfaces 26 of the cap seat 24, as well as
[0089] an outer surface 32, opposite to the support surface 30 and
having the same curvature as the curvature of the cylindrical outer
surface 23 of the terminal body 6,
[0090] wherein, with the cap 27 being positioned in the cap seat
24, the outer surface 32 of the closing portion 28 makes a
cylindrical continuity of the cylindrical outer surface 23 of the
terminal body.
[0091] In order to prevent an incorrect angular positioning of the
cap 27, the shape and position of the positioning surfaces 26 and
the shape and position of the counter-positioning surfaces 31 are
such to allow the insertion of the closing portion 28 into the cap
seat 24 in planned angular position, e.g. in two angular positions
rotated by 180.degree..
[0092] Advantageously, the closing portion 28 has an extension
parallel to the support surface 30 in the extension direction of
the counter-positioning surfaces 31, which is greater than a
distance between the two counter-positioning surfaces 31.
[0093] Preferably, the closing portion 28 and the cap seat 24 both
have a rectangular shape.
[0094] Along two first opposite sides (of the rectangular shape) of
the closing portion 28, the outer surface 32 and the support
surface 30 are spaced apart from each other by the
counter-positioning surfaces 31, and along two second opposite
sides (of the rectangular shape) of the closing portion 28, the
outer surface 32 and the support surface 30 meet at a common edge
with an acute angle, which may be sharp or slightly rounded.
[0095] Similarly, along two first opposite sides (of the
rectangular shape) of the cap seat 24, the bottom 25 of the cap
seat 24 and the cylindrical outer surface 23 of the terminal body 6
are spaced apart from each other by the positioning surfaces 26,
and along two second opposite sides (of the rectangular shape) of
the cap seat 24, the bottom 25 and the cylindrical outer surface 23
meet at a common edge with an obtuse angle, which may be sharp or
slightly rounded.
[0096] This makes it easy to make the cap by injection molding and
the cap seat 24 can be easily machined by flat milling.
Furthermore, the volume and mass of the cap 27 and also the amount
of waste material removed from the terminal body 6 can be kept very
low.
[0097] The anchoring protrusion 29 may comprise a number of
flexible tongues, adapted to elastically engage the longitudinal
hole 12 of the shear bolt 1.
[0098] In order to reduce or avoid the formation of electrical
charges at the geometric discontinuities of the terminal body 6 at
the transversal holes 22, it is advantageous to form caps 27 made
of electrically conductive polymer material, e.g.:
[0099] extrinsically conductive polymer (ECP), filled with
electroconductive metal powders (e.g. copper) or graphite, or
[0100] intrinsically conductive polymers (ICP), also called
semiconductor polymers, in which the polymer is filled with
electron-acceptor substances which increase the number of
electronic gaps, e.g. polymers with a polyenic structure, e.g.
polyparaphenylene (PPP), polyparaphenylenesulphide (PPS),
polyparaphenylenvinylene (PPV), polyaniline (PANI), polypyrrole
(PPy), polythiophene (PT), polyisothiaphene (PITN) and
polyethylenedioxythiophene (PEDOT).
[0101] A person skilled in the art will appreciate that the
features of the cap 27 and of the cap seat 24 of the terminal body
6 while being in synergy with some features of the shear bolt 1,
are advantageous even if applied to junction devices with shear
bolts different from the shear bolt 1 described hereto.
* * * * *